Merit Abrasives ZIRC Plus R801 PowerLock Cloth Discs-Type III Self-sharpening, zirconia alumina abrasive with grinding aid provides cooler , longer life on hard to grind materials. Durable, Y-weight, 2-ply polyester backing stands up to demanding applications. Type TR/III fit roll-on/roll-off plastic attachment system. All QC cloth discs are designed to run on back-up pads that are rated at or above the RPM of the grinder. Pack of 1